The Thin Blue Line

Earth's thin atmosphere is all that stands between life on Earth and the cold, dark void of space. This image, taken by astronauts aboard in the International Space Station in 2008, shows light from our Sun as it passes through these layers of gases that are held to the planet by Earth's gravity. Our planet's atmosphere has no clearly defined upper boundary, but instead gradually thins out into space. Most of the visible light from the Sun, as well as ultraviolet and infrared light, passes through the Earth's atmosphere. The atmosphere protects from more harmful types of light—such as X-rays and gamma rays—given off by cosmic sources.